Communication device

ABSTRACT

Communication device comprising a transmitter and a receiver, coupled to antenna means respectively via a transmitter output and a receiver input. For an effective and reliable reduction of transmitter leakage signals occurring at the receiver input corrective signal means are being used, comprising transmitter leakage signal selective amplifying means for selectively amplifying said transmitter leakage signal provided with a transmitter signal reference input being coupled to the transmitter output, a transmitter leakage signal input being coupled to the receiver input and a transmitter leakage signal output being coupled to said transmitter leakage signal input for a negative feed back of said transmitter leakage signals.

The invention relates to a communication device comprising a transmitterand a receiver, coupled to antenna means respectively via a transmitteroutput and a receiver input, as well as corrective signal means arrangedfor reducing a transmitter leakage signal at the receiver input andprovided with a transmitter signal reference input being coupled to thetransmitter output.

Communication devices of such type, also being referred to astransceivers, are known e.g. from U.S. Pat. No. 5,444,864. In particulartransceivers with single antenna means for transmission and receptionrequire specific filtering between antenna, transmitter output andreceiver input to protect the receiver during the transmission phase.The isolation between the transmitter output and the receiver inputshould be high enough to guarantee that the blocking voltage at thereceiver input is not reached even under worst case situations where theoutput power of the transmitter is set to its maximum level and thereflection coefficient of the antenna reaches its maximum value due tobody effects. In the known communication device use is made a.o. of a socalled diplexer interconnecting the antenna means the receiver input andthe transmitter output for the purpose of directing signals received bythe antenna means to the receiver input and signals to be transmittedfrom the transmitter output to the antenna means. To cancel the portionof the transmitter signal arriving at the receiver input, e.g. vialeakage through the diplexer or electromagnetic radiation coupling,hereinafter also referred to as transmitter leakage signal use is madeof a so called signal canceler, functioning as said corrective signalmeans. The signal canceller is to generate a cancellation signal, whichis a substantially gain and phase matched estimate of the transmitterleakage signal measured at the receiver put and which is fed forward tothe receiver input signal path via a summer, in which it is subtractedfrom the leakage transmitter signal.

However, the concept of signal cancellation applied in the knowncommunication device is highly demanding with regard to the accuracy andperformance of the circuitry needed. For example, the conformity inphase and amplitude between the cancellation signal on the one hand andthe leakage transmitter signal on the other hand is critical for aproper cancellation. Small mutual deviations strongly degrade thecancellation and may even result in an increase of transmitter leakagesignal. Apart therefrom, this known concept require the provision ofcircuitry, which inevitably cause unwanted side effects to occur, suchas the summer, which inherent to its function strongly reduces theoverall signal to noise ratio of the communication device.

It is a first object of the invention to overcome the above drawbacks ofthe conventional communication device and to increase the performancethereof.

A second object of the invention is to improve the sensitivity of thereceiver in full duplex mode.

According to the invention a communication device comprising atransmitter and a receiver, coupled to antenna means respectively via atransmitter output and a receiver input, as well as corrective signalmeans arranged for reducing a transmitter leakage signal at the receiverinput and provided with a transmitter signal reference input beingcoupled to the transmitter output, is therefore characterized in thatthe corrective signal means comprises transmitter leakage signalselective amplifying means arranged for selectively amplifying saidtransmitter leakage signal, a transmitter leakage signal input beingcoupled to the receiver input and a transmitter leakage signal outputbeing coupled to said transmitter leakage signal input thereby forming anegative feed back of the transmitter leakage signal occurring at thereceiver input.

The invention is based on the recognition that the phase and gainrequirements to obtain an effective reduction of the transmitter leakagesignal in a feed back loop are much easier to comply with than those tobe complied with by the cancellation signal in a feed forward reductionof the transmitter leakage signal. Where the cancellation signal in theknown communication device has narrowly match the transmitter leakagesignal in gain and phase, the gain of the leakage transmitter signal inthe feedback loop according to the invention only has to be sufficientlylarge, whereas its phase only has to be reversed, i.e. shifted over afixed 180°, to obtain an effective reduction thereof. Furthermore, thefeedback concept allows to dispense with circuitry introducing unwantedside effects such as a summer.

A preferred embodiment of such communication device is characterized inthat the transmitter leakage signal selective amplifying means comprisea phase splitter, an input thereof being coupled to the transmitteroutput, supplying respectively in-phase (I) and quadrature phase (Q)components of a transmitter signal to reference signal inputs of firstand second demodulators, as well as to carrier signal inputs of firstand second modulators, said first and second demodulators having atransmitter leakage signal input in common with a transmitter leakagesignal terminal of the corrective signal means being coupled to thereceiver input, and outputs being coupled respectively through first andsecond low pass filters to modulating signal inputs of said first andsecond modulators, an output of said modulators being coupled in commonto the transmitter leakage signal inputs of said first and seconddemodulators and phase inverting means being included in the signal pathof the transmitter leakage signal selective amplifying means.

By applying this measure, the pair of I and Q transmitter outputsignalcomponents, are respectively used in the first and seconddemodulators as a demodulators as a demodulation signal for asynchronous quadrature demodulation of the transmitter leakage signaloccurring at the receiver input, resulting in I and Q basebandtransmitter leakage signalcomponents. After a baseband selection in saidfirst and second low pass filters, these I and Q baseband transmitterleakage signalcomponents are re-modulated using the I and Q transmitteroutput signalcomponents as modulation carrier signals. The so obtainedre-modulated I and Q transmitter leakage signalcomponents are negativelyfed back to the receiver input. The phase inversion needed therefore isprovided by said phase inverting means and can be applied anywhere inthe loop, i.e. in the baseband or in the RF part of the loop.

For a combination of the re-modulated I and Q transmitter leakagesignalcomponents into a single transmitter leakage signal at thereceiver input without introducing signal distorsion or noise,preferably the first and second modulators each comprisetransconductance amplifying means an output thereof being coupled incommon to the receiver input and the transmitter leakage signal inputsof said first and second demodulators.

Another preferred embodiment of a communication device according to theinvention is characterized in that the transmitter leakage signalselective amplifying means provides a non-linear, input signal amplitudedependent amplification of the selected transmitter leakage signal. Thismeasure allows to adapt the degree of reduction of the transmitterleakage signal to its degrading effect on the receiver input signal,therewith saving power while maintaining optimum performance.

Preferably, the non-linear amplification is being provided by dead zonecontrol means coupled between the first and second low pass filters onthe one hand and the first and second modulators on the other handproviding in-phase and quadrature phase components of a basebandmodulation signal having a dead zone for amplitude variations of therespective output signals of the first and second lowpass filters withina range between predetermined first and second threshold levels, thein-phase and quadrature phase components of said baseband modulationsignal are varying in amplitude with the respective output signals ofthe first and second lowpass filters for amplitude variations beyondsaid range.

Dead zone signal amplification is on itself known e.g. from U.S. Pat.No. 4,277,695. The use thereof in accordance with the above measureallows to adjust the operative range of the corrective means and totrade off noise against receiver performance degradation.

Preferably, said dead zone is being determined by the maximum allowablereceiver input voltage. As a result thereof the operation of thecorrective means is switched off for those transmitter leakage signals,which are acceptable and do not lead to performance degradation,hereinafter also referred to as desensitization. In said switched offstate, the corrective means is prevented from reducing the signal tonoise ratio of the receiver input signal.

Another preferred embodiment of a communication device according to theinvention is characterized by a duplex filter having first and secondstages, the transmitter output being coupled through said first stage tothe antenna means, the antenna means being coupled through said secondstage to the receiver input and to the transmitter signal referenceterminal of the corrective signal means.

This measure further improves the performance of the communicationdevice mainly in that a reduction in sideband noise is obtainedtherewith.

Another improvement in noise performance is achieved by an attenuatorcoupled between the antenna means and the transmitter leakage signalinput of the corrective signal means.

Yet another preferred embodiment of a communication device according tothe invention is characterized in that said dead zone control meanscomprises first and second in-phase signal splitters and first andsecond quadrature phase signal splitters for splitting said dead zonein-phase and quadrature phase components of the baseband modulation intopositive and negative in-phase and positive and negative quadraturephase components, said positive, respectively negative, components beingsupplied to cool inputs of first variable transconductor amplifiers ofthe first and second modulators, respectively through and second phaseinverters to second variable transconductor amplifiers of the first andsecond modulators, outputs of said first variable transconductoramplifiers and outputs of said second variable transconductor amplifiersthrough third and second phase inverters being coupled to thetransmitter leakage signal terminal of the corrective signal means.

This measure allows to combine the re-modulated positive and negativein-phase and positive and negative quadrature phase RF transmitterleakage signalcomponents into a single feed back transmitter leakagesignal without using a resistive voltage summing circuit, therewithpreventing this combination from degrading the signal to noise ratio atthe receiver input.

Preferably, variable transconductor amplifiers are used only for theamplitude varying ones of the positive and negative in-phase andpositive and negative quadrature components of the dead zone basebandmodulation signal. This results in a reduction of circuitry needed foran effective implementation of the communication device.

The above and other object features and advantages of the presentinvention will be discussed in more detail hereinafter with reference tothe disclosure of preferred embodiments and in particular with referenceto the appended Figures, that show:

FIG. 1 a schematic diagram of a communication device according to theinvention;

FIG. 2 a blockdiagram of a preferred embodiment of a communicationdevice according to the invention;

FIG. 3 a blockdiagram of alternative corrective means for use in thecommunication device of FIG. 1 or 2;

FIG. 4 a characteristic diagram of the output control signal of the deadzone means for use in the communication device of FIG. 1, 2 or 3;

FIG. 5 a vector diagram illustrating the reduction of transmitterleakage in a communication device according to the invention;

FIG. 6 a vector diagram illustrating the reduction of transmitterleakage in a communication device according to the invention when usinga non-ideal quadrature phasesplitter.

FIG. 1 shows a communication device according to the inventioncomprising a transmitter T and a receiver R, coupled respectively via atransmitter output To and a receiver input Ri to an input and an outputof a duplex filter DF, an input/output terminal thereof being coupledvia a bidirectional link to antenna means ANT. The communication devicealso comprise corrective signal means C for reducing a transmitterleakage signal Vl leaking through to and occurring at the receiver inputRi. The corrective signal means C is provided with a transmitter leakagesignal terminal Tl being coupled to the receiver input Ri and with atransmitter signal reference input Tri being coupled to the transmitteroutput To. The corrective signal means C comprise transmitter leakagesignal selective amplifying means A having a transmitter leakage signalinput Tli coupled to the transmitter leakage signal terminal Tl forsupplying thereto the transmitter leakage signal Vl occurring at thereceiver input Ri. A transmitter leakage signal output Tlo of theselective amplifying means A is commonly coupled with the transmitterleakage signal input and the transmitter leakage signal terminal Tl,therewith closing a feedback loop. The selective amplifying means Aprovides for a selection, amplification (e.g. with factor α) and phaseinversion or 180° phase shift of the transmitter leakage signal Vl,resulting in an output signal, in the given example −αVl, which is fedback to its transmitter leakage signal input effecting the transmitterleakage signal in the loop, i.e. the transmitter leakage signaloccurring at the receiver input Ri, to reduce to Vl/(1+α).

For the selection of the transmitter leakage signal Vl, the selectiveamplifying means A may comprise any type of active frequency controlledfilter arrangement using the transmitter output signal at thetransmitter signal reference input Tri to lock the resonance frequencythereof to the carrier frequency of the transmitter leakage signal to beselected. The selective amplifying means A may alternatively be based onphase splitting of the transmitter leakage signal Vl into its in-phase(I) and phase quadrature (Q) signalcomponents, followed by mutuallyseparated selection and amplification thereof and subsequentre-combination into a single transmitter leakage signal. This will befurther clarified with reference to FIGS. 2 and 3.

FIG. 2 shows a blockdiagram of a preferred embodiment of a communicationdevice according to the invention, in which elements corresponding tothose shown in FIG. 1 have same references.

The transmitter leakage signal selective amplifying means A comprise aphase splitter 10, an input thereof being coupled to the transmittersignal reference input Tri, for splitting the transmitter output signalinto a pair of in-phase (I) and phase quadrature (Q) signalcomponentsand for supplying those respectively to reference signal inputs of firstand second demodulators 1 and 2, as well as to carrier signal inputs offirst and second modulators 7 and 8. Said first and second demodulators1 and 2 both have an input in common with the transmitter leakage signalinput of the transmitter leakage signal selective amplifying means A andthe transmitter leakage signal terminal Tl of the corrective signalmeans C and provide for a synchronous quadrature demodulation of thetransmitter leakage signal into a pair of baseband I and Q transmitterleakage signalcomponents. Outputs of the first and second demodulators 1and 2 are respectively coupled through first and second low pass filters3 and 4 for a selection of said baseband I and Q transmitter leakagesignalcomponents to first and second dead zone control means 5 and 6providing for a non-linear amplification of said baseband I and Qtransmitter leakage signalcomponents. The so amplified baseband I and Qtransmitter leakage signalcomponents are thereafter respectivelysupplied to first and second modulators 7 and 8 providing a re-modulatedpair of I and Q transmitter leakage signalcomponents, which are combinedat the transmitter leakage signal output of the selective amplifyingmeans A into one single re-modulated transmitter leakage signal. Thecircuitry 1, 3, 5, 7 and the circuitry 2, 4, 6, 8 therewith respectivelyform I and Q signal paths of the transmitter leakage signal selectiveamplifying means A, in which the I and Q transmitter leakagesignalcomponents are being processed mutually separated. There-modulated transmitter leakage signal is negatively fed back to theinput of the transmitter leakage signal selective amplifying means Athrough a phase inverter 9.

The dead zone control means 5 and 6 provide zero output for any signalsupplied to their input having a magnitude smaller than a certainpredetermined threshold level, and provide high gain amplification (α)to input signals having a magnitude greater than said threshold level.This means, that for magnitudes of the transmitter leakage signalssmaller than said threshold level the corrective means are notoperative, this effect also being referred to as desensitization of thecorrective means. By choosing said threshold level to correspond to themaim receiver input voltage, a desensitization in correctinginsignificant transmitter leakage signals is obtained, which does notdegrade the overall receiver performance, while maintaining an effectivereduction of significant transmitter leakage signals. Saiddesensitization furthermore prevents noise from being introduced in thereceiver input signal. This all considerably increase the powerefficiency as well as the sensitivity of the receiver when operating infull duplex mode.

The duplex filter DF may be constituted by a Fujitsu D5CG type duplexfilter having a transmitter related portion DFT, also referred to asfirst stage, coupled to a receiver related portion DFR, also referred toas second stage, the common connection between those stages beingcoupled in common to the antenna means ANT and to an input of anattenuator ATT. An output of the attenuator ATT is coupled to thetransmitter sign reference input Tri of the corrective signal means C.The transmitter output signal is supplied through the transmitterrelated portion DFT prior to the use thereof signal in the transmitterleakage signal selective amplifying means A as demodulation,respectively modulation signal. This results in a reduction of sidebandnoise at the receiver input. The attenuator ATT further improves theoverall performance of the communication device.

FIG. 3 shows a blockdiagram of alternative corrective means for use inthe communication device of FIG. 1 or 2, in which elements correspondingto those shown in FIG. 1 have same references. The first and secondmodulators 7 and 8 are formed by respectively a pair of positive andnegative controllable operational transconductor amplifiers 7′ and 7″and a pair of positive and negative controllable operationaltransconductor amplifiers 8′ and 8″, signal inputs thereof beingrespectively coupled to the I and Q outputs of the phase splitter 10 andsignal outputs thereof being fed back in common to the input of thetransmitter leakage signal selective amplifying means A, i.e. the commoninput of the demodulators 1 and 2. The baseband I and Q transmitterleakage signalcomponents selected by the low passfilters 3 and 4 andamplified in the dead zone control means 5 and 6 are now being used tovary the gain of the respective operational transconductor amplifiers7′, 7″, and 8′, 8″. Said operational transconductor amplifiers have noprovision to deal with change in signal polarity of the gain controlsignal. To overcome this restriction, the dead zone control means 5 and6 provide for a splitting of the signals to be processed on the basis oftheir polarity. This will be clarified with reference to FIG. 4. Thedeadzone control means 5 and 6 are provided with positive and negativeoutput terminals 5+ and 5−, respectively 6+ and 6−, the transfercharacteristic of the deadzone control means 5 and 6 from their inputsto their respective positive output terminals 5+ and 6+ beingrepresented by a solid line s and the transfer characteristic of thedeadzone control means 5 and 6 from their inputs to their respectivenegative output terminals 5− and 6− being represented by a dotted lined. For input signal magnitudes smaller than a predetermined thresholdvalue Vth, the signals CPI, respectively CPQ, at the output terminals5+, 5−, 6+ and 6− have zero value. Positive baseband I and Q transmitterleakage signalcomponents selected by the low passfilters 3 and 4 havingan amplitude increasing beyond +Vth will generate an outputsignalCPI/CPQ of the deadzone control means 5 and 6 at their respectivepositive output terminals 5+ and 6+ following the solid line curve s ofFIG. 4. Negative baseband I and Q transmitter leakage signalcomponentsselected by the low passfilters 3 and 4 having an amplitude decreasingbelow −Vth will generate an outputsignal CPI/CPQ of the deadzone controlmeans 5 and 6 at their respective negative output terminals 5− and 6−following the dotted line curve d of FIG. 4. The threshold value Vth ispreferably chosen to correspond to the maximum receiver input level.

The magnitudes of the output signals of the operational transconductoramplifiers are mutually similarly varying with the gain control signals,whereas their phase is either in-phase or in anti phase with their inputsignals. By choosing the operational transconductor amplifiers 7′ and 8′to vary in anti-phase with their input I transmitter leakagesignalcomponent and the operational transconductor amplifiers 7″ and 8″to vary in-phase with their input Q transmitter leakage signalcomponenta phase inversion is realised without the need for separate phaseinverting means, such as the phase inverter 9 in FIG. 2.

FIG. 5 shows a vector diagram illustrating the reduction of transmitterleakage in a communication device according to the invention as shown inFIGS. 2 and 3, in which Vl represents the transmitter leakage signaloccurring at the receiver input Ri without the corrective signal meansC. The I and Q components of this transmitter leakage signal Vl, i.e.Vli and Vlq respectively, are separately suppressed in the I and Qsignal paths to result in a suppressed transmitter leakage signal havinga magnitude at most substantially equal to the maximum receiver inputlevel, which is acceptable and does not degrade the performancenoticeably.

The phase shift of the transmitter leakage signal Vl occurring in theduplex filter DF will in practise not vary over 360°. This means, thatnot all four output signals CPI/CPQ of the deadzone control means 5 and6 at their respective positive and negative I and Q output terminals 5+,5− and 6+, 6− will vary in magnitude. Dependent from the I/Q phasequadrant(s), the vector representing the transmitter leakage signal Vloccurring at the receiver input never enters, one or two of theoperational transconductor amplifiers 7′, 7″, 8′ and 8″ can be omitted.For example, if vector Vl only varies over a phase angle within thefirst I/Q phase quadrant (the projections of Vl on the I and Q axisbeing positive), than only transconductor amplifiers 7′ and 8′ areneeded and the operational transconductor amplifiers 7″ and 8″ can bedispensed with. This simplifies the implementation of the correctivesignal means. In general, the phase shift of the duplex filter DF can bemeasured once and dependent on this phase shift one or more of thetransconductor amplifiers 7′, 7″, 8′ and 8″ can be omitted.

FIG. 6 shows a vector diagram illustrating the reduction of transmitterleakage in a communication device according to the invention when usinga non-ideal quadrature phasesplitter 10. Despite of the non-orthogonalI/Q phase splitting, the corrective signal means according to theinvention remain to be effective, reducing the I and Q components of thetransmitter leakage signal Vl an acceptable magnitude.

1. A communication device comprising: a transmitter, a receiver, the transmitter and receiver being coupled to an antenna respectively via a transmitter output and a receiver input, and a signal corrector that is configured to reduce a transmitter leakage signal at the receiver input, characterized in that the signal corrector comprises a transmitter leakage signal amplifier that is configured to selectively amplify the transmitter leakage signal, wherein a transmitter signal reference input of the amplifier is coupled to the transmitter output, a transmitter leakage signal input of the amplifier is coupled to the receiver input, and a transmitter leakage signal output of the amplifier is coupled to the transmitter leakage signal input to provide a negative feedback of the transmitter leakage signal occurring at the receiver input, characterized in that the transmitter leakage signal amplifier comprises: a phase splitter, a first demodulator and a second demodulator, a first low pass filter and a second low pass filter a first modulator and a second modulator, and a phase inverter, wherein: an input of the phase splitter is coupled to the transmitter output, the phase splitter is configured to supply respectively in-phase and quadrature phase components of the transmitter output to reference signal inputs of the first and second demodulators, as well as to carrier signal inputs of the first and second modulators, the first and second demodulators include: transmitter leakage signal inputs in common with the transmitter leakage signal input of the signal corrector, and outputs coupled respectively through the first and second low pass filters to modulating signal inputs of the first and second modulators, an output of each of the first and second modulators is coupled in common to the receiver input and the transmitter leakage signal inputs of the first and second demodulators to form a feedback path to the receiver input, and the phase inverter is included in the feedback path to provide the negative feedback of the transmitter leakage signal occurring at the receiver input.
 2. The communication device according to claim 1, characterized in that the first and second modulators each comprise at least one transconductance amplifier, having an output that is coupled in common to the receiver input and the transmitter leakage signal inputs of the first and second demodulators.
 3. The communication device according to claim 2, characterized in that the transmitter leakage signal amplifier provides a non-linear amplification of the transmitter leakage signal, based on an amplitude of the transmitter leakage signal.
 4. The communication device according to claim 3, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 5. The communication device according to claim 3, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 6. The communication device according to claim 5, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 7. The communication device according to claim 3, further including a dead zone controller coupled between the first and second low pass filters and the first and second modulators that is configured to: suppress amplitude variations of the respective output signals of the first and second lowpass filters within a range between predetermined first and second threshold levels, and amplify the amplitude variations beyond said range.
 8. The communication device according to claim 7, wherein the range is based on a maximum receiver input voltage.
 9. The communication device according to claim 7, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 10. The communication device according to claim 9, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 11. The communication device according to claim 10, characterized in that the dead zone controller comprises a splitter that is configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the amplitude varying components thereof being supplied to control inputs of variable transconductor amplifiers included in the first and second modulators, and the outputs of the first and second modulators are coupled through phase inverting means to the transmitter leakage output of the signal corrector.
 12. The communication device according to claim 10, characterized in that: the dead zone controller comprises first and second in-phase signal splitters and first and second quadrature phase signal splitters that are configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the positive, respectively negative, components are supplied to control inputs of first variable transconductor amplifiers of the first and second modulators, respectively through first and second phase inverters to second variable transconductor amplifiers of the first and second modulators, and outputs of the first variable transconductor amplifiers and outputs of the second variable transconductor amplifiers are coupled through third and fourth phase inverters to the transmitter leakage output of the signal corrector.
 13. The communication device according to claim 9, characterized in that the dead zone controller comprises a splitter that is configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the amplitude varying components thereof being supplied to control inputs of variable transconductor amplifiers included in the first and second modulators, and the outputs of the first and second modulators are coupled through phase inverting means to the transmitter leakage output of the signal corrector.
 14. The communication device according to claim 9, characterized in that: the dead zone controller comprises first and second in-phase signal splitters and first and second quadrature phase signal splitters that are configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the positive, respectively negative, components are supplied to control inputs of first variable transconductor amplifiers of the first and second modulators, respectively through first and second phase inverters to second variable transconductor amplifiers of the first and second modulators, and outputs of the first variable transconductor amplifiers and outputs of the second variable transconductor amplifiers are coupled through third and fourth phase inverters to the transmitter leakage output of the signal corrector.
 15. The communication device according to claim 7, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 16. The communication device according to claim 15, characterized in that the dead zone controller comprises a splitter that is configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the amplitude varying components thereof being supplied to control inputs of variable transconductor amplifiers included in the first and second modulators, and the outputs of the first and second modulators are coupled through phase inverting means to the transmitter leakage output of the signal corrector.
 17. The communication device according to claim 15, characterized in that: the dead zone controller comprises first and second in-phase signal splitters and first and second quadrature phase signal splitters that are configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the positive, respectively negative, components are supplied to control inputs of first variable transconductor amplifiers of the first and second modulators, respectively through first and second phase inverters to second variable transconductor amplifiers of the first and second modulators, and outputs of the first variable transconductor amplifiers and outputs of the second variable transconductor amplifiers are coupled through third and fourth phase inverters to the transmitter leakage output of the signal corrector.
 18. The communication device according to claim 7, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 19. The communication device according to claim 2, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 20. The communication device according to claim 19, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 21. The communication device according to claim 2, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 22. The communication device according to claim 1, characterized in that the transmitter leakage signal amplifier provides a non-linear amplification of the transmitter leakage signal, based on an amplitude of the transmitter leakage signal.
 23. The communication device according to claim 22, further including a dead zone controller coupled between the first and second low pass filters and the first and second modulators that is configured to: suppress amplitude variations of the respective output signals of the first and second lowpass filters within a range between predetermined first and second threshold levels, and amplify the amplitude variations beyond said range.
 24. The communication device according to claim 23, wherein the range is based on a maximum receiver input voltage.
 25. The communication device according to claim 24, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 26. The communication device according to claim 25, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 27. The communication device according to claim 25, characterized in that the dead zone controller comprises a splitter that is configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the amplitude varying components thereof being supplied to control inputs of variable transconductor amplifiers included in the first and second modulators, and the outputs of the first and second modulators are coupled through phase inverting means to the transmitter leakage output of the signal corrector.
 28. The communication device according to claim 25, characterized in that: the dead zone controller comprises first and second in-phase signal splitters and first and second quadrature phase signal splitters that are configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the positive, respectively negative, components are supplied to control inputs of first variable transconductor amplifiers of the first and second modulators, respectively through first and second phase inverters to second variable transconductor amplifiers of the first and second modulators, and outputs of the first variable transconductor amplifiers and outputs of the second variable transconductor amplifiers are coupled through third and fourth phase inverters to the transmitter leakage output of the signal corrector.
 29. The communication device according to claim 23, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 30. The communication device according to claim 29, characterized in that: the dead zone controller comprises first and second in-phase signal splitters and first and second quadrature phase signal splitters that are configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the positive, respectively negative, components are supplied to control inputs of first variable transconductor amplifiers of the first and second modulators, respectively through first and second phase inverters to second variable transconductor amplifiers of the first and second modulators, and outputs of the first variable transconductor amplifiers and outputs of the second variable transconductor amplifiers are coupled through third and fourth phase inverters to the transmitter leakage output of the signal corrector.
 31. The communication device according to claim 29, characterized in that the dead zone controller comprises a splitter that is configured to split in-phase and quadrature phase components of the transmitter signal reference input into positive and negative in-phase and positive and negative quadrature phase components, the amplitude varying components thereof being supplied to control inputs of variable transconductor amplifiers included in the first and second modulators, and the outputs of the first and second modulators are coupled through phase inverting means to the transmitter leakage output of the signal corrector.
 32. The communication device according to claim 22, wherein the transmitter leakage signal amplifier is configured to: suppress amplitude variations of the transmitter leakage signal within a range between predetermined first and second threshold levels, and amplify the amplitude variations beyond said range.
 33. The communication device according to claim 32, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 34. The communication device according to claim 32, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 35. The communication device according to claim 22, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 36. The communication device according to claim 35, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 37. The communication device according to claim 1, further including a duplex filter having first and second stages, the transmitter output being coupled through the first stage to the antenna, the antenna being coupled through the second stage to the receiver input and to the transmitter signal reference input of the signal corrector.
 38. The communication device according to claim 37, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 39. The communication device according to claim 1, further including an attenuator coupled between the antenna and the transmitter signal reference input of the signal corrector.
 40. The communication device according to claim 39, characterized in that the transmitter leakage signal amplifier provides a non-linear amplification of the transmitter leakage signal, based on an amplitude of the transmitter leakage signal. 